Method of making selenium rectifiers



, Patented Aug. 24, 1948 or MAKING ssLaNmM.

asc'rmsas METHOD Wayne E. Blackburn, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.

Application November 10, 1948. Serial No. 509,817

12: Claims. (Cl. 175-388) My application relates to selenium rectiiiers and radiation sensitive devices and, in particular. relates to methods of producing selenium coatings which are free from microscopic cracks and holes for such rectifiers.

The process of making selenium devices which has been conventionalin the prior art has been to coata metal plate with selenium; then to heat it to a temperature of the order of 170 C. to change the selenium coating fromthe less conductive modification to the more conductive modification; and to thereafter apply a conductive metallic coating to the exterior face of the selenium layer. A considerable fraction of the elements :i'ormed by this process were found, upon subsequent test, to break down with the accompaniment of what might be termed a miniature explosion, leaving crater-like holes between the base plate and the conductive layer. While units which hadsuffered such breakdowns could be used subsequently for useful purposes, they \were always. liable to suffer subsequent breakdowns. and were by no means as reliable as units in which such breakdowns had not occurred.

Investigation of the nature of such breakdowns led to the. discovery that they were due to the existence of filaments or projections of the sprayed metal of the contact layer which had passed through small cracks and crevices produced in the selenium film by the annealing.

which shall be free from the above-described effects.

' my method, I dip into a bath of molten selenium Another object of my invention is to provide a a metallic plate, which preferably is of iron, having va sandblasted surface which has subsequently been nickel-plated. The dipping process abovementioned can conveniently be carried out by mounting disks having central holes in spaced pairs upon a spindle, the latter being rotated, dipped into the selenium and then removed therefrom. The rotation of the disks ensures that centrifugal force will remove the excess of selenium, and leave a coating which is of substantially uniform thickness over the entire disk. Preferably, I dissolve in the selenium about 0.1% by weight of the element bromine. Ithen allow the disks to cool to substantially room tempera ture and Schoop spray onto their surfaces a contact layer of pure cadmium. Thereafter. I anneal the units at substantially C. for at least six hours. After such annealing, I impress between the base plate and the contact layer of each unit a. direct-current voltage tending to cause electrons to flow from the selenium to the cadmium. when first applied, this voltage has a value of about 12 volts, and is gradually increased to 32 volts.

Selenium units made by the'foregoing method. in which the contact layer is applied to the selenium while the latter is in its nonconductive condition, I have found to be free from projections of the metallic contact layer through the selenium toward the metallic base plate: and the short circuits and production of miniature craters, which occur in a case of a considerable percentage of units formed by the prior art method of annealing the selenium before the contact layer is applied, are entirely absent.

I claim as my invention:

1. The .method of making selenium devices which comprises the steps of coating a conductive surface with a layer of amorphous selenium; coating the free surface of this amorphous selenium layer with a conductive contact layer and thereafter annealing the selenium.

2. The method of making selenium devices which comprises the steps of dipping a conductive surface into molten selenium, reducing the selenium layer to a substantially uniform thickness then coating the free surface of the selenium layer with a conductive contact layer and thereafter annealing the selenium.

3. The method of making selenium devices which comprises the steps of coating a conduc- 2,447,eao

tive surface with a layer of amorphous selenium: coating the outer surface of this amorphous selenium layer with a conductive contact layer and thereafter annealing the selenium for a period of the order of six hours at a temperature of the order of 170 C.

4. The method of making selenium devices which comprises the steps of coating 8'. conductive surface with a layer of amorphous selenium; coating the outer surface of this amorphous selenium layer with a conductive contact layer and thereafter annealing the selenium at a temperature of the order of 170 C.

5. The method of making selenium devices which comprises the steps of coating a conductive surface with a layer of amorphous selenium; coating the outer surface of this amorphous selenium layer with a conductive contact layer and thereafter annealing the selenium and applying an electrical forming-voltage to the selenium.

6. The method of making selenium devices which comprises the steps of coating a conductive surface with.a layer of amorphous selenium; coating the-outer surface of this amorphous selenium layer with a conductive contact layer and thereafter annealing the selenium at a temperature of the order of 170 C. and applying an electrical forming-voltage to the selenium.

7. The method of making units comprising a layer of selenium sandwiched between two layers of conducting material which comprises coating a conductive surface with amorphous selenium; coating the free surface of the amorphous selenium with a conductive material and thereafter annealing the selenium.

8. The method of making'units comprising a layer of selenium sandwiched between two layers of conducting material which comprises coating a conductive surface with amorphous selenium; coating the free surface of the amorphous selenium with a conductive material and thereafter annealing the selenium at a temperature of the order of 170 C.

9. The method of making units comprising a layer of selenium sandwiched between two layers of conducting material which comprises coating a conductive surface with amorphous selenium: coating the free surface of the amorphous selenium with a conductive material and thereafter annealing the selenium at a temperature of the order of 170 C. and applying a forming-voltage to the selenium.

10. The method of making selenium rectiflers which comprises dipping a rotated metallic plate into molten selenium and withdrawing it therefrom, then spraying the free surface of the selenium with a metallic contact-layer and annealing the selenium thereafter at a temperature of the order of 170 C.

11. The method of making selenium rectiflers which comprises dipping a rotated metallic plate into molten selenium and withdrawing it therefrom, then spraying the free surface of the selenium with a metallic contact-layer and anneal-' ing the selenium thereafter at a temperature of the order of 170 C. for a period of the order of six hours.

12; The method of making selenium rectiflers which comprises dipping a rotated metallic plate into molten selenium and withdrawing it therefrom, then spraying the free surface of the selenium with a metallic contact-layer and annealing the selenium thereafter at a temperature of the order of 170 C. and thereafter electrically forming the selenium by subjecting it to a gradually increasing voltage.

WAYNE E. BLACKBURN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

